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Al Schwartz
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Discussion Starter · #1 ·
Inspired by LS' descrition of his Pre-Add based Talbot Lago, I prepared a Ferrari 4.5 L for last year's Las Vegas meet. Following his lead, I built it on a brass chassis with a front mounted motor and used a typical spring coupling beteen the motor and the pinion shaft. About half way through the race, run on the Blue King, I heard the characteristic whine of metal spinning on metal and found my car proceeding, very slowly, along the main straight. The diagnosis was clear - the spring was spinning on the pinion shaft. A drop of CYA served as a temporary fix but enough time was lost so that the car finished at or near the bottom of the heap.

I have never been particulary successful in using these couplings outside of their as-manufactured installations - perhaps my home built alignment is less than perfect or my shafting is a poor match for the spring but, in any event, I have found them to be difficult to assemble and unreliable. The Ferrari was prepared with the long track in mind so it mounted a TSRF motor and had a heavy brass chassis - i.e. significant stress on the joint.

In a post re preparation for the Marconi Proxy, Larry Geddes showed his front-engined car with a coupling joint made up from a socket head cap screw and a ball-end Allen wrench. The cap screw was drilled to fit the motor shaft and the wrench was turned down to form the pinion shaft - brilliant - and, as it turns out, based on the Marconi results, very effective.

AS Tom Leherer sang: "Plagarize, plagarize, plagarize, let no on else's work evade your eyes" - so I copied it.

My usual source, McMaster Carr, supplied the cap screws and wrenches. The cap screw was chucked in the 3 jaw on my Unimat and drilled 2mm then the threads turned off and the head cut down (cosmetic -doesn't affect function) The wrench was cut and chucked close in the 3 jaw and a short section, about 4 mm, was turned down to shaft size. A bearing from a defunct motor was chucked in the tailstock and used as a support so the shaft could be further turned, leaving a shoulder to define the position of a flanged ball bearing.

Chassis with socket end on motor and pinion shaft before assembly:



Close-up:



and assembled:



How does it work? - for race performance - we'll see - but there is one measurement that is interesting - using current draw as a measure of load, I observed the following:

Motor alone - uncoupled: 0.25A @ 6 V
Motor + spring and pinion shaft (no crown gear) 0.34A @ 6V
Motor + new joint and pinioin shaft (no crown ) 0.27 A @ 6V

This suggests to me that (1) the motor/pinion shaft alignment is not perfect and (2), in the case of (1), the new joint is more efficient and has less loss than the spring. It is also much easier to assemble since the parts just slide together.

Without any permission, license or endorsement from Larry, I propose to call this the Geddes Joint - after all, we have Chapman struts, deDion rear ends and Prof Fate has attached his nom de guerre to a hinged front axle and I think that this innovation should be similarly recognized.

EM
 

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Brian Ferguson
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3,652 Posts
Very slick idea - sort of a 1/32 CV joint. Nice implementation, EM! If it hasn't been done before, then "Geddes Joint" it is!


I'd be interested in what you find out in terms of longevity for the mating parts. I imagine they should last quite a while as long as they are kept lubed and the misalignment isn't too severe.

Thanks for the info!
 

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Great Joint you have there Al.

But the same problem is lurking. How do you keep the two halves of the joint from spinning on the motor shaft or the rear axle half shaft. The same thing that happend with the spring arrangment. I grant you, it will be a sturdier arrangement as long as you can keep the coupling ends from slipping again.

I am lazy and like the spring setup and have not lost one out of about 10 I have used. But I learned early on to fasten the spring to the shafts either with a touch of solder or Blue or Red locktight. Depending on the horsepower of the motor being harnessed up. I find the Fly red spring from the Panoz or other front engine types to be the best and strongest I have found. So I think some Blue or Red locktight do will for you also. The Red can be a bear to get to let go, once setup, if you have to change out a component. but does the job very well.

I wish you well with this one though, nice job.



Larry S.
 

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Al Schwartz
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Discussion Starter · #4 ·
The socket bit is soldered to the motor shaft and the pinion is soldered onto the turned down part of the wrench bit. The shoulder locates it against the bearing which is a press fit into the support. A better way to do it would be to have the flange on the bearing on the other side but in this case, the motor needs to be angled into its support so the pinion shaft has to be fed from the back.

I agree that the spring/locktite combinatin should work and be equally free if the alignment is good - but I am a bit of a pepper tree mechanic and rather expect that i will always be a bit askew and this joint seems to be more tolerant.

It was fun to build but i know I'll be staring at your tailpipes anyway!

EM
 

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Good! solder does sound like the answer for you. But don't worry about looking at my tail pipes, unless I find some traction for the Talbot with those Ortmans. Have good horse power, traction, is a problem so far. But we shall see, as they say at Vegas!!!


Larry S.
 

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I don't think it's been done in 1/32 before, but Tamiya had a similar arrangement for the driveshafts in one of their "cheaper" 1/10 RC buggy kits (Grasshopper I think?) The halfshafts had large ball-end Allen type ends at both the differential and hub ends. The hub and differential had the cap-screw arrangment. There were rubber gaiters placed over the ends of the halfshafts prior to assembly.

I'm all for the name Geddes joint though!

Mark.
 

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Hi

Actually, It was Dan Wilson(ex of Russkit and MESAC in the 60s) who attached my name to the front.

As a matter of simplicity, would it not be simpler to just use a brass metric 2mm Id sleeve from K&S as your extension?

With all these 4.5 period cars coming out, you wanna start their own? I mean we have been lumping them into "the 50s"s. But here, the BRM, Lago etc versus my 4.5 Ferrari 375, Alfetta and all is possible. Or does anyone care?

Fate
 

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Al Schwartz
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Discussion Starter · #8 ·
I have been unfair to the spring couplings - and it's all a matter of almost converting inches to mm. When I first built the car, I used what I had on hand - some 0.781 (5/64") shaft and bearings. I noticed when I assembled the Geddes joint with Slot-It gears that I needed to solder the pinion to the shaft although they are designed for a press fit. I assummed that I had turned the shaft a bit undersize but I just remeasured it and it is spot on. However 5/64 is close but not exactly 2mm which converts, at 25.4 mm/inch, to 0.787" so the shaft was 0.006" undersize! This accounts not only for the slip fit of the pinion but also the slippage of the spring which was, I am certain, designed for a 2mm shaft.

Of course, here in the U.S., metric parts are the outliers and although 2mm bearings and shafts are available, they are 50% more expensive that the inch counterparts.

At the end of the day, I shall probably keep using the ball joint because (1) spring couplings aren't free, (2) the assembly-disassembly is easier and (3) I believe that they are a bit more tolerant of any misalignment than the spring - besides, I like the look!

Mantra: measure, measure, measure

EM
 

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Al Schwartz
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3,378 Posts
Discussion Starter · #9 ·
QUOTE As a matter of simplicity, would it not be simpler to just use a brass metric 2mm Id sleeve from K&S as your extension?

Yes, if you can get everything lined up perfectly, but, more to the point, when was the last time that you saw me do anything the simple way?

QUOTE With all these 4.5 period cars coming out, you wanna start their own? I mean we have been lumping them into "the 50s"s. But here, the BRM, Lago etc versus my 4.5 Ferrari 375, Alfetta and all is possible. Or does anyone care?

We should do at least one race that way. I love to see a line-up of cars that truly replicates an era. You have your 4CLT, Alfetta and 375, Larry has his Talbot, I have the V-16 BRM and a 375, we could reasonably sneak in a 163 if anyone has one and I have about decided to explore a front-motored Pre Add chassis for an Alfa or 4CLT.

Let's see what the performance envelope is and decide which track would be best.

(Note to those not familiar with the goings-on at the Las Vegas gathering - the emphasis is much more on finding combinations of cars and tracks that will provide a good race than it is on winning and cars are shared about among the participants with the clear understanding that racing cars can and often will be broken but if the purpose is just to put them on shelves - why bother with motors?)

EM
 

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Hi

EM, you FORGOT!

Remember when that mad man Russell did those 4 exquisite '37 Alfas and sent us all one? Well, Russell in correspondence with me, discovered an ovewhelming affection for the Merc 154/163. I had been promisng myself that I would take the old MRRC and convert it to the 163. Turned out Russell had 2 bodies done by a friend of his in glas, and sent me one. I built a simple brass pan chassis with a "Fate Front end" for the Marconi and an RX41. PdL has used this car TWICE to spank us on the short track. The year we did the 30s race on both the short track and the King, PdL decided he wanted the superior handling and giving up about 30 feet on the straight, still finished first on the short track and, I think 3ed on the long track with that car. THEN, last fall running on the Model Car Racing test track, I used the same car to turn faster times than any of the cars in their Modern F1 test without magnets!
I was always fond of the idea that one of these ran(badly) at indy in 48 and 49 as well. The americans who "liberated" the car had no idea how to brew the fuel!
Once while racing a Lancia, someone accused me of "baby duck syndrome", that is I loved 50s F1s and indy cars because those were the first proper race cars I saw. But I love the 30s racers and while an old guy, I am not old enough to have seen THESE cars(although you are!).

Anyway, I guess if we want to run a "post WW2 class" but pre-2.5s, we have a track full of cars between us!

Fate
 
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